Method of creating NC data for grooving

ABSTRACT

NC data for grooving are created by inputting a groove shape (GR) which lies on a three-dimensional curved surface as well as a groove-depth specifying curve (GRC) which indicates a relationship between a distance d from one end and groove depth hk of a point at this distance, obtaining the distance dk from one end of the groove-depth specifying curve (GRC) in accordance with 
     
         dk=lk·Lj/Li 
    
     where Li represents the total length of the groove shape, lk the distance from one end of the groove shape and Lj the total length of the groove-depth specifying curve (GRC), obtaining, from the groove-depth specifying curve, the depth hk at the distance dk from the abovementioned one end, and adopting the groove depth hk as groove depth of a point at the distance lk from the one end of the groove shape (GR).

TECHNICAL FIELD

This invention relates to a method of creating NC data for grooving.More particularly, the invention relates to a method of creating NC datafor grooving in cases where groove depth varies, wherein use is made ofgroove curve data specifying a groove shape on a three-dimensionalcurved surface and groove depth data (a groove depth pattern) specifyingthe depth of the groove.

BACKGROUND ART

There are cases where it is desired to cut a groove in athree-dimensional curved surface.

FIG. 6 is a view for describing a prior-art example of such groovingmachining. SS denotes a three-dimensional curved surface, GR a groove,and Mk (k=1, 2, . . . ) a series of points on the three-dimensionalcurved surface specifying the groove GR. Grooving machining entailsobtaining the coordinates of the series of points Mk specifying thegroove GR, subsequently obtaining the coordinates of a series of pointslower than the abovementioned coordinates by the dimension h of groovedepth along the -Z axis, creating NC data based on these coordinates,and cutting the groove based on the NC data.

In the prior art, the groove depth dimension h is fixed at all times.Consequently, the coordinates of the series of points on the groovebottom can be obtained automatically and the NC data for grooving can becreated with ease. However, if the groove depth dimension h varies, thecoordinates of the series of points on the groove bottom cannot be foundautomatically but must be calculated manually by the operator.Accordingly, creating NC data for cutting a groove having a varyingdepth is a troublesome task.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a grooving NC datacreation method through which NC data for cutting a groove can becreated in a simple manner even if groove depth varies.

NC data for grooving are created by: (a) inputting a groove shape whichlies on a three-dimensional curved surface as well as a groove-depthspecifying curve which indicates a relationship between a distance dfrom one end of the groove and groove depth hk of a point at thisdistance, (b) obtaining the distance dk from one end of the groove-depthspecifying curve in accordance with

    dk=lk·Lj/Li

where Li represents the total length of the groove shape, lk thedistance from one end of the groove shape and Lj the total length of thegroove-depth specifying curve, (c) obtaining, from the groove-depthspecifying curve, the depth hk at the distance dk from theabovementioned one end, and (d) ng the groove depth hk as groove depthof a point at the distance lk from the end of the groove shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) schematic explanatory views of the method of thepresent invention;

FIG. 2 is a block diagram of an apparatus for practicing the method ofthe invention;

FIG. 3 is a flowchart of processing according to the method of theinvention;

FIGS. 4 and 5(a) and 5(b) are views for describing the method of thepresent invention; and

FIG. 6 is a view for describing the method of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS 1(a) and 1(b) are schematic explanatory views of the method of thepresent invention. FIG. 1(a) is a sectional view in an X-Z planeillustrating the shape of a groove, and FIG. 1(b) is an explanatory viewof a groove-depth specifying curve (groove depth pattern) whichindicates the relationship between a distance dk from one end of thegroove and a groove depth hk.

SS represents a three-dimensional curved surface, GR a groove, TL atool, CVi a planar curve on the X-Y plane for specifying groove shape,GRC a groove-depth specifying curve (groove depth pattern) on the H-Vplane, Pk a point on the curved surface SS of the groove GR, Pk' aprojected point obtained by projecting the point Pk onto CVi, Pk" amachining point on the groove bottom and corresponding to the point Pk,Li the total length of the planar curve CVi, and Lj the total length ofthe groove-depth specifying curve GRC. It should be noted that groovedepth gradually becomes larger from 0 up to a certain distance dkm andthen gradually becomes smaller.

FIG. 2 is a block diagram of an automatic programming apparatus forpracticing the method of the present invention. Numeral 101 denotes akeyboard for data input, 102 a processor, 103 a ROM for storing acontrol program, 104 a RAM, 105 a working memory, 106 a memory forstoring grid points of meshes specifying the curved surface SS andcreated NC program data for grooving machining, 107 an output unit foroutputting to an external storage medium 108 such as a paper tape ormagnetic tape, the created NC program data for grooving machining, 109an address bus, and 110 a data bus.

FIG. 3 is a flowchart of processing for creating NC data for grooving inaccordance with the method of the present invention. The method of thepresent invention will now be described in accordance with the flowchartof FIG. 3. It is assumed that the three-dimensional curved surface SShas been specified by a number of meshes and that the curved surface hasalready been stored in the RAM 104. As for the method of specifying thethree-dimensional curved surface SS, refer to FIG. 6 as the relateddescription in the specification of International ApplicationPCT/JP86/00100 (filed on February 28, 1988 and entitled "Method ofCreating Complex Curved Surfaces"). Further, it is assumed that severaltypes of groove-depth specifying curves [see FIG. 1(b)] also have beenstored in the RAM 104, and that it is arranged so that the operator canmake a selection in accordance with the shape of the groove.

First, the operator considers the shape of the groove to be machined,selects a predetermined specifying curve, e.g., the groove-depthspecifying curve GRC shown in FIG. 1(b), from among the several types ofgroove-depth specifying curves prepared. The operator then enters, fromthe keyboard 101, the planar curve CVi, which is obtained by projectingthe groove shape GRC to be formed on the curved surface SS onto the X-Yplane (step 201).

The processor 102 obtains the total length Lj of the designatedgroove-depth specifying curve GRC and the total length Li of the enteredplanar curve CVi (step 202), and performs the following operation (step203):

    k←1

Next, the processor 102 projects a k-th point Pk', at a predeterminedpitch, onto the planar curve CVi of the three-dimensional curved surfaceSS. The process 102 then obtains and stores the coordinates (xk,yk,zk)of the point Pk at the intersection with a mesh MS (see FIG. 4) forspecifying the three-dimensional curved surface SS stored in the RAM 104(step 204), and obtains a distance lk from the starting point of theplanar curve CVi to the point Pk' (step 205). For a method ofcalculating the intersection point Pk, see FIG. 7 and the relateddescription in the abovementioned International ApplicationPCT/JP86/00100.

Next, the distance dk from one end of the groove-depth specifying curveGRC corresponding to the distance lk is obtained in accordance with theequation

    dk=lk·Lj/Li

The groove depth dimension hk at the distance dk is obtained from thegroove-depth specifying curve GRC, and the groove depth dimension hk isadopted as the groove depth of point Pk on the three-dimensional curvedsurface SS (step 206).

Thereafter, if the tool TL is capable of being moved by simultaneousthree-axis control along the X, Y and Z axes, the coordinates(xk,yk,zk-hk) of the point Pk" located below the point Pk by the groovedepth dimension hk along the -Z axis, as shown in FIG. 5(a), areobtained. If the tool TL is capable of being moved by simultaneousfive-axis control along the X, Y, Z axes, a horizontal rotational axis(B axis) and a vertical rotational axis (C axis), then the tool iscontrolled in such a manner that the vector of the central axis of thetool will point in the direction of the normal line at the point Pk, asshown in FIG. 5(b). Therefore, the point Pk" is obtained (step 207),which point is lower than Pk by the groove depth dimension hk along thedirection of the normal line. NC data are obtained by adopting the pointPk" as a machining point, and the data are stored in the memory 106(step 208).

The processor 102 determines whether the point Pk' is the end point onthe planar curve CVi (step 209). If point Pk' is not the end point, thenthe operation

    k←k+1

is performed (step 210) and processing from step 204 onward is repeated.If Pk' is the end point, end processing, such as withdrawing the tool TLa designated distance from the curve surface SS, is executed (step 211).

In the foregoing, the groove depth dimension hk is obtained by using thetotal length Li of the planar shape obtained by projecting the grooveshape to be machined on the curved surface SS onto a predeterminedplane, as well as the distance lk from one end of the planar shape.However, it is permissible to adopt an arrangement in which the groovedepth dimension hk is obtained by adopting Li as the total length of theactual groove shape on the curved surface, and using the distance lkfrom one end of the groove shape.

Thus, in accordance with the invention, the arrangement is such that NCdata for grooving are created by specifying a groove shape GR which lieson a three-dimensional curved surface as well as a groove-depthspecifying curve which indicates a relationship between a distance dfrom one end and groove depth hk of a point at this distance, obtainingthe distance dk from one end of the groove-depth specifying curve inaccordance with

    dk=lk·Lj/Li

where Li represents the total length of the groove shape, lk thedistance from one end of the groove shape and Lj the total length of thegroove-depth specifying curve, and adopting the groove depth hk at dk asthe groove depth of a point at the distance lk from the one end of thegroove shape. This makes it possible to simply create NC data forcutting a groove having a varying depth.

We claim:
 1. A method of creating NC data for grooving athree-dimensional curved surface, comprising the steps of:specifying agroove shape which lies on the three-dimensional curved surface;specifying a groove-depth specifying curve defining a relationshipbetween a distance dk measured from one end of said groove shape and agroove depth hk of a point at said distance dk; obtaining said distancedk in accordance with

    dk=lk·Lj/Li

where Li represents a total length of said groove shape, lk represents adistance from said one end of said groove shape and Lj represents atotal length of said groove-depth specifying curve; obtaining, based onsaid groove-depth specifying curve, said groove depth hk at saiddistance dk; and creating NC data for said grooving at said distance dkbased on said groove depth identifying a groove depth of a point at thedistance lk from said one end of said groove shape.
 2. A method ofcreating NC data for grooving according to claim 1, further comprisingthe steps of:selecting said total length Li to represent a total lengthof said groove shape projected onto a predetermined plane; and selectingsaid distance lk to represent a distance from one end of said projectedshape.
 3. A method of creating NC data for grooving according to claim2, storing a plurality of groove-depth specifying curves; andspecifyinga groove-depth specifying curve by selecting a predetermined one of thestored groove-depth specifying curves.
 4. A method of creating NC datafor grooving the three-dimensional curved surface with a tool accordingto claim 2, further comprising the step of:performing grooving inaccordance with said NC data so that a distal end of the tool is loweredby hk at said distance lk.
 5. A method of creating NC data for groovingaccording to claim 2, further comprising the step of:performing groovingin accordance with said NC data so that the tool is oriented normal tothe three dimensional curved surface by simultaneous five-axis control,and so that a distal end of the tool is lowered by hk along the normaldirection.